The prior art for controlling transmission stages by utilizing road data stored in a navigation system mounted on a vehicle includes Japanese patent publication No. 6-272753 and Japanese patent laid-open publication No.7-234991 which have proposed a control device that controls the transmission stage based on various items of information, including vehicle speed variation and degree of accelerator opening, that can be detected by sensors, and map information read out from the navigation system. Such a device provides the vehicle with an optimum transmission stage in conformity to the varying drive conditions.
With the above-described prior art transmission control devices, road data is obtained from the navigation system in order to determine a transmission stage in conformity with the condition of the road on which the vehicle is now running. However, all information used in such prior art control systems merely indicates the current drive conditions. With the prior art systems, it is not possible to control the transmission in anticipation of future changes in the drive conditions.
For example, when the vehicle goes up a slope, the prior art control devices can not change a transmission stage until the vehicle goes up to a certain level that results in a change in an actual vehicle speed or degree of accelerator opening. Moreover, this prior art control, while following the road information neglects the driver's will or intention. More specifically, the transmission stage control based on the road information has a good adaptability to surrounding conditions, but tends to force a perfunctory control on the driver.
Further, the above-described prior art control device encounters a difficult problem if there is a difference between the detected vehicle position detected by a current vehicle position sensor and the actual vehicle position.
Furthermore, when a transmission shift change pattern is controlled based on road data for example, a up-shift is prohibited during driving around a corner or a bend in the road, whereas shift change points become higher during high-speed driving. However, the prior art transmission control devices can not control the transmission when the vehicle is driving around a corner at high speed.
In most cases, there are multiple conditions for the road, for example, a curved highway or speedway, and a climbing straight-away with a low friction coefficient, and the prior art devices can not provide suitable transmission control when. driving on such a road.
Accordingly, it is an object of this invention to achieve vehicle control that conforms well to the driver's intention, and more particularly to provide a vehicle control device that achieves more favorable control in response to a driver's decelerating operation.